Pricing is almost always based on volume, no matter what product or what industry.
As business people, we are all always searching for the best deal on our supplies. All this guy has done is bucked up to get a better deal on his supplies. It's my understanding that you have to be spending well into the 6 figures to buy direct, so, if you are willing to commit to that sort of volume and dollars, I have no doubt that 3M would be happy to sell directly to you as well. If you not, you really don't have anything to complain about, to 3M anyways.
In my area, there are 3 or 4 shops that can buy direct from 3M, and it is all consumed within their own shops. The funny part of it is, they are some of the more expensive shops to get signage done at. All they are doing is maximizing profit margins.
Fair has nothing to do with business.